US1027062A - Pneumatic hammer. - Google Patents

Description

R. AQNORLING.

PNBUMATIO HAMMER.

APPLICATION I'ILED DEO.17, 1910.

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R. A. NORLING.

PNEUMATIC HAMMER. APPLIOATION FILED DBO. 17,1910.

Patented May 21, 1912.

4 SHBETSSHEBT 4.

' UNITED STATES P1TENT OFFICE.

REINHOLD A. NORLING, OF AURORA, ILLINOIS, ASSIGNOR TO AURORA AUTOMATIC MACHINERY COMPANY, OF AURORA, ILLINOIS, A. CORPORATION OF ILLINOIS.

PNEUMATIC HAMMER.

Specification of Letters Patent.

Patented May 21, 1912.

. Application filed December 17, 1910. Serial No. 597,864.

To all whom it may concern:

Be it known that I, Ilium-torn A. NOIKIING, a citizen of the United States, and a resident of Aurora, in the county of Kane and State of Illinois, have invented certain new and useful Improvements in Pneumatic Hammers; and I do hereby declare that the following is a full, clear, and exact description thereof, reference being bad to the accompanying drawings, and to the letters of reference marked thereon, which form a part of this specification.

This invention relates to a portable pneumatic tool or hammer of that class embracing a barrel or cylinder, a piston or plunger adapted to move therein, and a controlling valve, through which the air or other fluid under pressure is admitted to and permitted to escape from the opposite ends of the cylinder or barrel to give reciprocat-ory movement to the plunger therein.

The invention is illustrated and described herein as applied to a chipping hammer, otherwise known as a short stroke hammer and consists of the combination of parts hereinafter described and more particularly pointed out in the appended claims.

In the drawings :Figure 1 is a longitudinal section through the hammer in a plane containing the central axis of the barrel or cylinder and the central axis of the throttle valve chamber. Fig. 2 is a longitudinal section on an enlarged scale through the barrel ina plane through the central axis thereof at an angle to the plane of Fig. 1. Fig. 3 is a similar section through the barrel in the same plane showing the piston and movable valve member in different positions from those shown in Fig. 2. Fig. 4 is a longitudinal section through the central axis of the barrel in a plane at a second angle to the plane o the section of Fig. l. Figs. 5, (5, 7, and 8 are longitudinal sections through the barrel taken respectively on the lines 5-5, 6-'6, 77 and 8-8 of Fig. 9. Fig. 9 1s a rear end elevation of the barrel. Fig.

. 10 is a cross section through the head of the hammer on the line 10-10 of Fig. Fig. 11 is a cross-section on the line 11--11 of Fig. Fi 12 is a cross-section on the line on the line 14---11 of Fig. 1?). Fig. 15 is a longitudinal section through the valve block Fig. 14 is a trans-v verse scction through the valve block body body on the line 1515 of Fig. 14. Fig. 16 is a side elevation of the valve block cap. Fig. 17 is a transverse section through said valve block'cap on the line 17- 17 of Fig. 16. Fig. 18 is a longitudinal section through the valve block cap on the line 1818 of F1 17.

In that embodiment of my invention illustrated in the accompanying drawings, A represents the barrel'or cylinder of the hammer; B, the piston or plunger adapted'to reciprocate therein; C, the tool carrying nozzle; and D, the tool, in this case a chisel.

The rear end of the barrel or cylinder is screw-threaded as at a, to receive the for-' ward, internally threaded end of a hollow head E. Said hollow head E is closed at its rear end by an end wall E and has formed integrally with it a handle F. The head E is split atits forward end and provided with a longitudinal recess 6 inclosed by apertured lugs e, c which are drawn together by a bolt 0 so as to rigidly clamp the thread of the head in engagement with the thread of the barrel.

G indicates a transverse passage in the tool head containing a valve bushing g.

G is a throttle valve piston reeiprocably mounted in said bushing, and adapted to be operated by a stem G which projects through an aperture G into a slot G in the handle containing a pivotally mounted lever G which operatively engages the upper end of said stem. Said lever Gr is actuated by a hand lever or trigger F pivotally mounted in the slot G" in position to be engaged by the palm of the .hand when the tool handle is grasped and connected to said lever G by a link An annular chamber (1 is formed about the bushing g and is connected with the interior thereof by supply ports 9 g is an air passage leading to the annular chamber g. Said passage is enlarged at its outer end and threaded to receive the usual airsupply pipe (not shown). The outer end of the transverse passage G is closed by a threaded cap 9 and the opposing parts of said cap and of the piston valveGflare provided with recesses to receive the ends. of a coiled spring which normally holds the piston in position to close the supply ports J I The valve mechanism for controlling the admission and exhaust of air into and from the cylinder embraces a valve l)l()(7l( ll provided with exhaust and admission ports and so I an annular or cylindric valve ring J surrounding said valve block and arranged to slide endwise thereon to open and close said ports; said valve ring being provided with oppositely facing differential pressure areas. Said Valve block is located at the rear end of the barrel and is made in two parts,a body member H and a cap member I.

The valve block body ll rests at its forward end within an annular recess a formed in the rear end of the piston barrel A. It is provided with a longitudinal bore of a diameter slightly greater than that of the piston barrel A and co-axial therewith. A dowel pin it (see Figs. 2 and 3) holds said valve block body against rotative movement relativeto the piston barrel. The cap member I is provided at its forward end with a short annular projectionI which engages within the bore of the valve block body. Its rear end rests against the end wall E of the lunger barrel head. The valve block H is tius rigidly held in place between the rear end of the cylinder A and the end wall of the hollow head E. A dowel pin 2' (see Figs. 2 and holds the cap I against rotative movement relative to the valve block body H.

The valve member J is in the form of a cylindric slecve surrounding the valve block H" and is arranged to have cndwise sliding movement thereon. The valve block H is enlarged in diametcr at its forward end to form an annular flange H The valve ring J is enlarged at its forward end to embrace said flange H and is provided with an annular shoulder J on its'inner surface which is opposed to the rear face of the annular flange H and which forms the larger pressure area of the valve ring. The valve block cap I is made of larger diameter than the rear end of the valve block body H so as to form .a forwardly facing, annular shoulder '1 extending around the rear end of the body, and the valve ring J is enlarged at its rear end, as indicated at J*, to embrace said valve block cap. J indicates an annular rearwardly facing shoulder on the inner surface of the valve ring J opposite the forwardly facing annular shoulder I of the valve block.

ring has moved to the forward limit of its,

movement, as shown in Figs. 3 and 4. The forward movement of the valve ring J is limited, by the rear end of th e cylinder A, while its rearward movement is limited by the end wall E of the hollow head E. The

length of the valve ring J is so proportioned to the distance between the end wall E and the rear end of the cylinder A that the shoulders J and J 5 of the valve ring do not strike the shoulders of the valve block to which they are opposed when the valve ring moves to its limits, but leave asmall space between them (see Figs. 2 and 3) so that air may be readily admitted to the pressure areas of the valve ring.

K indicates a set of longitudinal exhaust passages formed in the wall of the barrel A near its rear end and extending into the wall of the valve block to an annnlarly arranged series of exhaust ports K which open through the outer surface of valve block near its forward end. Said exhaust ports are in the form of transverse slots in the outer surface of the valve block body H, there being a slot for each pair of longitudi- "nal ports K of which there are four pair as shown in the drawings (see Figs. 4, 7, 10 and 13). Said passages K communicate with the interior of the barrel by means of ports K near its rear end, which ports are open to the space X. about the valve, which space is freely open to the outer air through the passage X (see Fig. 1) which opens through the cylindric wall of the head E.

M indicates passages extending longitudinally through the walls of the main barrel or cylinder and which open into the interior of the barrel at its forward end through ports m (see Figs. 1, 5 and 10), and which are adapted for the exhaust bf air from the outer or forward end of the cylinder during the outward stroke of the piston. Said passages extend into the walls of the valve block H and each opens into a plurality, in this case four, longitudinal passages M of smaller diameter which extend into the valve 'stroke, the valve ring J being then in such position that the-ports K are uncovered and block cap I to points adjacent therear end en the valve ring J .is at the-rearward imitof its movement, the exhaust space X 1s connected with the mner orrear end of go'ng descriptionfit will be apparent that 15. space formed by the channel J of the valve air to the inner end of the cylinder.

- cap I, said ports extending from the chamber I? through the outer surface of said cap and being inclined slightly to a plane at right angles to the longitudinal central axis of the cap so as to open into the annular ring in all positions thereof. (See Figs. 2, 3 and 4). The space formed by the channel J is thus always supplied with live air when the throttle valve is open.

In the rear end of the Valve block body.

H are provided a series of annularly arranged radial orts R,whichexte-nd through the walls ofsald valve block body and constitute the'main supply ports for admitting Said ports are adapted. to be uncovered and brought intocomnmnication with the annular groove or channel J of the valve ring J for the admission of air to the inner end of the cylinder when the valve ring J is in its forward position. (See Fig. 4).

'N indicates a longitudinal passage (see Figs. 1, 5, 8, 15 and 18) formed in the wall of the cylinder Aand extending through the valve block body H and into-the cap I where it connects at its rear end with one of the radial ports I leading from the live air chamber I in said cap. N is a parallel longitudinal passage formed in the wall of the chamber A and spaced circlunferentially from the passage N. Said passage N extends through the valve block body-II and opens at its rear end through a port N opening. through the outersurt'ace of the valve block body into the space between the annular shoulder J, that is to say, the

smaller pressure area of the valve ring,

and the annular shoulder l of the valve block. At their forward ends the passages N and N are connected by a transverse slot 11. 'formed in the inner surface of the barrel. The smaller pressure area of the valve ring when the piston B is'in a position to cover the slot or is thus subjected to the live air pressure by reason of the live air passing through the port N the passage N, the slot n, the passage N and the connected radial port I' which opens into the live air chamber l' in the valve block cap.

- Some of the longitudinal exhaust passages M which lead to the fQl'WtlI'tl end of the barrel, as shown in the drawings two ct each four located on opposite sides of the alve block, open by ports I (see'higs. 1,

16 and 17 into slots P formed in the outer cylindric surface of the valve block cap I and spaced longitudinally to the rear of the exhaust portsM. The slots 1 open into the live air space formed by the groove or channel J when the valve ring J is in its rearward position and are closed by said valve ring when the same is in its outer or forward position. The slots P ports P and the longitudinal passages M M connected therewith, constitute the supply ports for admitting air to the outer or forward end of the cylinder to drive the piston rearward on its return stroke.

Q indicates a longitudinal supply passage formed in the wall of the cylinder A and extending into the valve block body and opening by a port Q into the space between of the piston B on its power or forward stroke just prior to its completion of said stroke, so as to permit. the live air in the rear end of the cylinder to act on the larger pressure area of the valve ring and shift said ring against the live air pressure on its I smaller pressure area, to its rearward position. The passage Q is extended forwardly beyond the port Q to a point intermediate said port and the forward end of the cylinder where itopens into said cylinder through a' second port Q, which is closed by the pisston when the port Q, is uncovered to admit live air to shift the valve ring rearwardly, and which is uncovered by the forward end of the piston on its return stroke. Au auxiliary longitudinal exhaust passage T is formed in the wall of the cylinder, said passage opening at its rear end by a port 'I (see Figs. 2 and 8) through the wall of the rear end of said cylinder into the exhaust space X and opening at its forward end by a port T into the cylinder at a point longitudinally spaced to the rear of the port Q and adapted to be uncovered by the forward end of the piston on its return stroke after it has uncovered the port Q. By this construction the passage (Q. leading to the larger pressure area J of the valve ring is connected to the exhaust space X after the forward end of the piston has passed .the port 'l on the return stroke, through the port Q, the cylinder, the port 'l-'. the passage T and the port '1. This relieves the live air pressure on the larger pressure area of the valve ring, so that it may be shifted to its forward position by live air pressure on its smaller pressure area when the rear .end of the piston reaclzcs and int-lows the slot v u, and the live an", passing through &

' pressure area.

The operation of the valve mechanism is as follows: Starting with theparts in the position indicated in Fig. 4, with the plunger at the inner or rear end of its stroke, and the valve rmg J at the outer. or forward supply of air is thus admitted to drive the limit of its movement, the main supply ports R for admitting live air to the rear end of the cylinder are open into the channel or groove J of the valve ring and the exhaust ports M through which the exhaust from the forward end of the cylinder passes to the exhaust space X are also open. The opening of the throttle valve G admits live air to the live air chamber 1 in the valve block cap I whence it passes through the radial ports I in said cap to the channel or groove J and thence, through the ports R to the inner end of the cylinder. A large piston with force forwardly on its working or power stroke, and the air at. the forward end of the cylinder in advance of the piston is exhausted through the ports m, the passages M, M and the exhaust ports M As the piston nears the end of its forward stroke and reaches the position indicated in Fig. 3, its forward end covers the port Q? and its rear end uncovers the port Q thus permitting the live air at the inner end of the cylinder to pass through the passage Q, and port Q to the larger pressure area J" of the valve ring. This etlfccts a movement of the valve ring J to the rearward limit of its movement against the live air pressure on its smaller pressure area J which it receives through the port N the passage N the slot a, the passage N and the associated port I" in the valve block cap. This rcarward movement of the valve ring uncovers the exhaust ports 1 for the rearend of the cylinder, opens the supply ports P adapted to admit live air to the forward end of the cylinder, into communication with the channel or groove J of the valve ring which contains live air, and closes the exhaust ports M and the main supply ports R adapted, respectively, for the exhaust from the forward end of the cylinder and for the supply of live 'air to therear end of the cylinder. In the meantime the piston has reached the outer or forward limit of its movement-and under the pressure of live air passing through the ports P and the associated passages and ports P M M and m, is driven on its return or rearward stroke.

Atthe beginning of the return stroke and prior to-the time the piston reaches the position indicated by dotted lines in Figs. 1 and 2, the live air entering the rear end of the cylinder through the passage N and the associated radial port I in the valve block cap, escapes with the rest of the exhaust from the rear end of the cylinder through the exhaust ports K so that it has no efiect on the smaller pressure area J 5 of the valve ring. Just before the piston reaches the last referred to position, its forward end uncovers the ports Q and T thereby opening the larger pressure area J 1 to the exhaust space X, through the port Q}, the passage Q, the port Q the cylinder, the port T and the auxiliary exhaust passage and ports T, T, so that, when it reaches the said position and its forward end incloses the slot n so as to direct the live air entering through the passage N into the passage N and thence through the port N to the smaller pressure area J of the "alve ring, a forward movement of said valve ring is efiected since there is now no pressure on the large pressure area of the valve ring. This puts the parts in the first position described with the exhaust ports K for the inner or rear end of the cylinder and the supplyv ports P for the forward end of the cylin-- der closed, and the supply ports Rfor the inner or rear end of the cylindepi-and the.

exhaust portsM for the outer or forward end of the cylinder open. Thi operation thencontinues as before. i I

The ports K which connect the .trior of the cylinder with the exhaust passages for the exhaust from the inner or rear end of the cylinder are located, as shown in the drawings, forward of the rear end of the cylinder A and in such position that they will be closed on the return stroke by the rear end of the piston '13 almost immediately after said rear end of the piston has inclosed' the slot at so as to direct the live air to the smaller pressure area of the valve ring J to effect its forward movement The piston thus'imrnediatcly cuts off the exhaust from the inner or rear end of the cylinder, independently of the action of the valve ring J, so that the air still remaining in the rear end of the cylinder will be compressed by the piston as it finishes its return stroke and Will'act as an air cushion. lVhile this arrangement is not essential, since the valve ring J is shifted by live air in both directions, still it is preferable, inorder to prevent any possibility of the piston striking the valve block cap, in case the action of the valve should be slow for any reason, as

when it becomes gummed or when the throttle valve is but slightly opened so that only a small amount of air is admitted to shift the valve ring.

pressure area of the valve, with the space between the annular shoulder formed b the I flange H of the valve block body an the stant one, for though the smaller pressure annular shoulder .J or larger pressure area of the valve. This is provided in order to start the tool when the piston is at the outer or forward limit of its movement and the valve ring is in its forward position, as may happen when the tool is idle and is held in a vertical position with its forward end down, and the valve ring falls by gravity into the position referred to.

It will be seen from this description that the controlling valve of m improved hammer is a valve of difi'erentlal area in which the pressure on both areas of the valve is intermittent, neither pressure being a conarea is always open to live air pressure, the live air, by reason of the slot n has no effect onthe smaller pressure area during the return stroke of the piston since it escapes during the return stroke of the piston from the passage N through the slot 11. into the cylinder and thence with the rest, of the exhaust through the exhaust ports for the inner end of the cylinder. At one instant only, namely, at the time when the valve is shifted from its outer to its inner position, pressure is exerted on both ends of the valve.

I claim as my invention 1. The combination with a cylinder and a reciprocating plunger therein, of a controlling valve for controlling the admission and exhailst of air into and from the cylinder embracing an annular valve having oppositely facing differential pressure areas,-

means controlled by the plunger for admitting live air to the larger pressure area of the valve, and means affording a contlnuous passageway for live air to the smaller pressure area of the valve, said means including a port opening into the cylinder and adapted to be closed by said plunger. when the rear end of the cylinder is open to the exhaust.

2. The combination with a cylinder and a reciprocating plunger therein, of a controlling valve for controlling the admission and exhaust of air into and from the cylinder embracing-a valve block provided with a live air chamber in its rear end, a valve ringhaving oppositely facing differential pressure areas, means controlled by the plunger for admitting live air to the larger ressure area of the valve, and means affordmg a continuous passageway from said live air chamber to the smaller pressure area of the valve, said means including a port opening into the cylinder near its rear end and adapted to be closed by the piston when it approaches the end of its return stroke.

3. The combination with a cylinder and a reciprocating plunger, of a controlling valve for controlling the admission and exhaust her at its rear end and a hollow valve having op Jositely facing differential pressure areas a apted to move endwise on said valve block, said valve block having two longitudinally spaced sets of exhaust and supply ports near its opposite ends, the sets of admission ports being adjacent, a channel formed in said hollow valve adapted, in the endwise movement thereof, to communicate with each setof admission ports in alternation, means providing a constant supply of live air to said channel, means controlled by the piston for admitting live air to the larger pressure area of the valve, and means afi'ording a continuous passageway from said live air chamber in the valve block to the smaller pressure area of'said valve, said means including a port opening into the cylinder and adapted to be closed by the piston on its rc- I ing oppositely facing differential pressure areas adapted to move endwisc on said valve block, saidvalve'block having two longitudinally spaced sets of exhaust and admission ports near its opposite ends, the sets of admission ports bein adjacent, a channel formed in said hollow valve adapted, in the endwise movement thereof, to communicate with each set of admission ports in alternation, supply ports in said valve block connecting said live air chamber with the channel in said hollow valve in all positions thereof, means controlled by the piston for admitting live air to the larger pressure area of the valve, and means affording a continuous passageway from said live air chamber in the valve block to the smaller pressurearea of said valve, said means including a port opening into the cylinder and adapted to be closed by the piston on its return stroke.

5: The combination with a cylinder and a reciprocating plunger therein, of a controlling valve for controlling thcndmission and exhaust of air into and from the cylinder embracing an annular valve having oppositely facing dili'crenlial pressure areas, means controlled by the plunger for mlmitting live air to the larger pressure area of the valve, a passageway open at its rear end to a constant supply of live air, a second passageway adapted to supply air to the smaller pressure area of said valve, and a (having oppositely facing difierential pressure areas and being adapted to move endwise on said valve block, said valve block member having shoulders of different areas opposing the pressure areas of said valve ring, a circumferentially extending channel in said valve ring located at the rear of the smaller pressure area thereof, means providing a constant supply of live air to said channel, and admission ports in said valve block member located on opposite sides of the shoulder thereof of smaller area, said valve ring being constructed to connect said channel in its endwise movement with said ports in alternation.

7. In combination with a cylinder and reciprocating plunger therein, of a controlling valve controlling the admission and exhaust of air into and from the cylinder, embracing an annular valve having oppositely facing difierential pressure areas, means affording a continuous passageway for live airto the smaller pressure area of the valve, said means including a port opening into the cylinder and adapted to be closed by said plunger when the rear end of the cylinder is open to the exhaust, and means for controlling the pressure on the larger pressure area of the valve, embracing a passageway opening at its rear end by a port leading to said larger pressure area and opening at its forward end into the cylinder by an admission port and by an exhaust port, the exhaust port being spaced forwardof the admission port, said admission port being adapted to be uncovered by the rear end of the piston on its outward stroke, and said exhaust port being adapted to be covered by the forward end of the piston on its outward stroke and to. be uncovered thereby on its return stroke.

8. The combination with a cylinder and a reciprocating plunger therein, of a controlling valve for controlling the admission and exhaust of air into and from the cylinder embracing an annular valve having oppositely facing differential pressure areas, means controlling the supply of air for the smaller pressure area of said valve embracing a passageway open at its rear endto a constant supply of live air, a second passageway adapted to supply air to the smaller pressure area of said valve, and a slot opening into said cylinder and connecting the forward ends of said passageways, said slot being adapted to be closed by the piston on its return stroke, and means for controlling the pressure on the larger pressure area of the valve, embracing a passageway opening at its rear end by a port leading to said larger pressure area and opening at its forward end into the cylinder by an admission port and by an exhaust port, the exhaust port being spaced forward of the admission port, said admission port being adapted'te be uncovered by the rear of the piston on its outward stroke. and said exhaust port being adapted to be covered by the forward end of the piston on its out ward stroke and to be uncovered thereby'on' its return stroke prior to the time that said slot is covered by the rear end of the piston,

9. The combination. with a cylinder and a reciprocating plunger therein, of a controlling valve for controlling the admission and exhaust of air into and from the cylinder embracing a bearing member formed at the inner'end of the cylinder and 27 valve ring" adapted to slide thereom'said valve ring having oppositely facing, differential pressure areas and being adapted to move endwise on said bearing member, said bearing -member having two longitudinally spacedshoulders of different areas opposing the pressure areas of said valve ring, a circumferentially extending channel in said valve ring located atthe rear of the smaller pressure area thereof, means providing a constant supply of'live air to said channel, ex-

haust ports located at opposite ends of the valve bearing member for the exhaust respectively from the rear end and from the forward end of the cylinder, and longitudinally spaced admission ports located intermediate the ends of said bearing member adapted for the supply of air respectively to the rear and to the outer end of said cylinder, said channel in said ring member ber ing constructed to communicate with said admission ports in alternation when said,

valve ring member is at the opposite'lilnits f its movement.

10. The combination with a cylinder and a reciprocating plunger therein, of a controlling valve for controlling the admission and exhaust of air into and from the cylinder embracing a valve block located at the rear end of thecyliuder and a valve ring adapted to slide thereon, said valve ring having oppositely facing, differential pressure areas and being adapted to, move endwise on said valve block, and said valve block having two longitudinally spaced shoulders. of different areas opposing the pressure areas of said valve ring, a circumferentially extending channel in said valve ring located at the rear of the smaller pressure area thereof, a live air chamber located in the rear end of said valve block, 'ports connecting said live air chamber with the respectively from the rear end and from the forward end of the cylinder, and two longitudinally spaced sets of admission orts located intermediate the ends of said hearing member adapted for the supply of air respectively to the rear and to the outer end of said cylinder, said channel in said ring members being constructed to communicate with said sets of admission ports in alternation when said vlave ring member is at the opposite limits of its movement.

11. The combination with a cylinder and a reciprocating plunger therein, of a controlling valve for' controlling the admission and exhaust of air into and from the cylinder embracing a valve block located at the inner end of the cylinder and a valve ring adapted to slide thereon, said valve ring having oppositely facing, differential pressure areas and being adapted to move endwise on said valve block, and said Valve block com n'ising a body member bored to form a prolongation of said cylinder and amp member inclosing the rear end of said cylinder, said valve block having two longitudinally spaced shoulders of dltl'erent areas o :iposing the pressure areas of said,

valve ring, a. circumfercntially extending channel in said valve ring located at the roar of the smaller pressure area thereof, a live air chamber in said valve block cap, ports in said valve block cap connecting said chamber with said channel of said valve ring in all positions thereof, exhaust and supply ports for the inner end of the cylinder lo cated respectively at the forward and rear ends of said valve block body, and exhaust and admission ports for the forward end of the cylinder 10 ated in said valve block cap, the admission ports for both ends of the cylinder being longitudinally adjacent, and said channel in said ring member being construeted to communicate with said admission ports for the opposite ends of the cylinder in alternation when said valve ring member is the opposite limits of its movement.

12. The combination with a cylinder and a reciprocating plunger therein, of a controlling valve for controlling the admission and exhaust of air into and. from the cylinder embracing a valve block located'at the inner end of the cylinderand a valve ring. adapted to slide thereon, said valve block comprising a body having a bore forming a prolongation of the cylinder and a cap member closing said bore, said valve ring having oppositely facing, differential pressure areas adapted to move endwise on said valve block, and said valve block having two longitudinally spaced shoulders of ditlerent areas opposing the pressure areas of said valve ring, a circumferentially extending channel in said valve ring located at the rear of the smaller pressure area thereof,

means providing a constant supply of live air to said channel, a set of exhaust. and admission ports for the rear end of the cylinder opening through the outer surface of the valve block body respectively at its forward and rear ends, an exhaust passage leading from the forward end of the cylinder and opening at a point near the rear end of the valve block cap by a port through the annular surface thereof, and an admission port connected with said exhaust passage and opening through the outer annular surface of said cap at a point forward of said exhaust port, said channel in said. ring member being constructed to communicate with said admission ports for the forward and rear ends of the cylinder in alternation when said valve ring member is at the opposite limits of its movement.

In testimony that I claim the foregoing as my invention I atlix my, signature in the presence of tvo witnesses, this 5th day of December A. I). 1910.

REINIIOLD A. NORLING.

Witnesses Ivan A. .IlANssnN, Lns'r'nfi J. YOUNG.

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